Hey,
Growlin and other vocal techniques come with practise. While your voice is developing, im sure with practise you will be able to growl and perform other vocal techniques. For now be careful if you are trying to growl as if done incorrectly, you can damage your vocal chords and that leads to problems!.
Singers such as Shirley.C and Aretha can deliver gut wretchin growls and billowing vibrato's, but their voices are well matured. All comes with practise :wink: